Bushings are available in increments of .001" from .185" through .199" and .218" through .343". The easiest way to tell the bushing size needed is to measure your loaded rounds at the neck. This caliper or micrometer reading indicates bullet diameter plus twice the thickness of the neck. The bushing diameter must measure less than this, we suggest .002" to .003" smaller. Taking into account the spring-back of the case neck after sizing, this would give you .001" to .002" “grip” on the bullet.